library("tidyr")
library("dplyr")
library("ggplot2")

data("diamonds")
diamonds %>% summary
diamonds %>% str
diamonds %>% head

w <- diamonds %>% group_by(clarity) %>% 
	summarise(prumerna.cena = mean(price))
w
w %>% arrange(prumerna.cena)
w %>% arrange(desc(prumerna.cena))

w %>% 
	filter(rank(prumerna.cena) == 3) %>% 
	select(clarity)

diamonds %>% 
	group_by(clarity, color) %>% 
	summarise(prumerna.cena = mean(price)) %>% 
	arrange(desc(prumerna.cena))

diamonds %>% 
	group_by(clarity, color) %>% 
	summarise(
		prumerna.cena = mean(price), 
		Q25 = quantile(price, probs = 0.25), 
		Q75 = quantile(price, probs = 0.75)
		) %>% 
	arrange(desc(prumerna.cena)) %>% 
	print(n = 60)

a <- diamonds %>% 
	group_by(clarity, color) %>% 
	summarise(
		prumerna.cena = mean(price)
		) %>% 
	arrange(desc(prumerna.cena)) %>% 
	print(n = 60)

a %>% spread(key = "clarity", value = "prumerna.cena")
a %>% spread(key = "color", value = "prumerna.cena")